Transcript Population growth - Global Change Consulting Consortium, Inc.

Forecasting global
biodiversity threats
associated with human
population growth
Population growth
World Population
Number of Individuals
75
70
65
km)
Density (person per sq.
World Population Density
60
55
50
45
40
2000
2010
2020
2030
2040
9,500,000,000
9,000,000,000
8,500,000,000
8,000,000,000
7,500,000,000
7,000,000,000
6,500,000,000
6,000,000,000
2050
2000
Year
2000
2004
2050
2010
2020 2030
Year
Birth rate
Death rate
21.2(/1000)
17.5(/1000)
13.8(/1000)
8.8(/1000)
8.7(/1000)
9.7(/1000)
Growth rate
1.25
0.88
0.42
Density
46.4
57.4
69.3
2040
2050
Introduction
Background
• Possible threats to ecosystems are
human density and population growth
• However population growth rate is not
a good estimator of exact threat
• Biodiversity still shown to relate to
human population size
Past studies
• Density of humans related to
threatened bird species (Kerr & Currie
1995) and threatened plant species
(Thompson & Jones 1999)
Current study
• Based in relationship between human
density and threats to biodiversity a
statistical model was built to predict
future threats
• The model included population data
and ecological characteristics of
various nations
Methods
Data utilized
• Total number of mammal and bird species data as reported by nation
according to UNEP-WCMC Animals of the World Database
• IUCN Red List of 2000 on critically endangered, endangered and vulnerable
species
• Mean annual temperature per nation
• Mean annual precipitation per nation
• Human census data for 2000, 2020 and 2050 from U.S. Census Bureau
• Tested 114 of 230 nations review
– small and island nations excluded
– some nation’s data incomplete
Methods
Analysis
• Chose potential variables that would
be significantly correlated with a
number of threatened species
• To account for nation size all
frequency variables were divided by
geographic area in 106 km2
• Variables log-transformed to normalize
distributions
• Subset of predictor variables chose for
multiple regression analysis
Results
Table 1. Linear regression correlates of the number of threatened mammal and bird
species per unit area (log 10)
•
•
•
Human population density significantly correlated with threatened species
per unit area { r2 = 0.402 P < 0.001}
Greatest correlation with species richness
Mean precipitation correlated, but temperature did not
Results
•Fig. 1. Predicted vs.
actual values of logtransformed density of
threatened species per
nation for the year 2000
based on the multiple
regression model: log
threatened species per
106 km2=-1.534+0.691 ×
log species
richness+0.259 × human
population density.
•
Linear regression model showed human population and species richness good
combined predictors
Results
•
•
•
•
•
Growing populations show increased threat to species, while declining
populations show slight decrease in threat
Median increase = 1.6 by 2020 and 3.0 by 2050
Largest increase threat due to high species diversity and growth rate of
3.19% is in Congo with 26 additional threatened species by 2050
United States has possible increase of 10 threatened species by 2050
although growth rate is 0.91%
Although 100 of 114 nations show increase of threat by 2020, 10 of those
show decrease in threat by 2050
Results
•
Fig. 2: Forecast changes in number
of mammal and bird species
threatened for each of the 114
nations in 2050.
Discussion
•
•
•
•
•
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Model demonstrates that 87.9% of differences in number of threatened
species can be accounted for by human population density and species
richness
The other 12.1% not explained by density could be due to endemic species
Climate change and economic from growth could also affect biodiversity
Model can be used to project threat of extinction based on population
growth
Model needs to be expanded: Brazil’s threatened species were
underestimated showing that population density within a country cannot
always account for threat alone without including demands of other
countries
Ultimately shows that if model can be projected to other taxa then there is a
serious threat to biodiversity worldwide